1. Field of the Invention
The present invention relates to a bar-code reading apparatus and a bar-code reading method.
2. Description of the Related Art
A bar-code reading apparatus, which reads information encoded as a bar code through a scanning of the bar code with a laser beam and the like, has been widely used. Such a bar-code reading apparatus detects a change in optical characteristics of light reflected from the bar code and generates bar-code width data which shows a width of each element constituting the bar code. The bar-code reading apparatus then performs a decoding processing based on the bar-code width data, thereby reading the information encoded as the bar code.
Here, a bar-code reading processing which is generally executed in the bar-code reading apparatus will be explained. The bar-code reading apparatus uses a sensor to receive light reflected from the bar code, performs a current-to-voltage conversion (hereinafter, referred to as “I/V conversion”) on a current signal corresponding to an amount of the received light, and generates an I/V conversion signal. The bar-code reading apparatus then performs a differential processing on the I/V conversion signal and obtains a differential signal. Next, the bar-code reading apparatus fixes, as a reference voltage value, a voltage value at a predetermined position of a signal-invariant region which does not include any extreme values in the differential signal, and processes the differential signal based on the reference voltage value to obtain a peak hold value as a voltage value at a peak and a bottom hold value. Then, the bar-code reading apparatus divides the voltage of the peak hold value and the bottom hold value which are calculated based on the reference voltage value by a predetermined ratio, and sets a threshold value signal which is to be a threshold value. After that, the bar-code reading apparatus compares the voltage value of the differential signal with the threshold value signal in sequence, and determines that the signal having a level not less than the threshold value signal should be the peak. Then, the bar-code reading apparatus generates a comparison signal based on a peak width of each peak, and regenerates the bar-code width data based on the comparison signal (see Japanese Patent Application Laid-Open No. S60-157678 and Japanese Patent Application Laid-Open No. 2001-28045).